In the art, air cushioning systems for shoes are generally known. For example, U.S. Pat. No. 7,395,615 discloses a pumping device for use in a shoe that includes a cushion body formed inside a sole of the shoe. The cushion body includes front and back air chambers disposed in the front and heel of the shoe, respectively. A pump is mounted adjacent to and in communication with the back air chamber and a suction valve and a check valve are mounted at the front and back sides of the pump to provide air to the back air chamber. A pressure adjusting valve provides a connection between the back air chamber and the front air chamber.
A further example of an air cushioning system is disclosed in U.S. Published Application No. 2005/0005473 which describes a shoe insert that functions to form a pumping chamber. Connected to the pumping chamber is an air inlet conduit as well as an air outlet check valve that leads to an air outlet conduit. When the pumping chamber is in a pumping mode during use, air is brought into the shoe from the outside via the air inlet conduit and circulated through the midsole and toe region of the shoe via the air outlet conduit.
Yet further, U.S. Publication No. 2007/0294916 discloses an air cushioning and circulation system for a shoe. The shoe is provided with first and second air rooms that are formed in the front and rear of the shoe, respectively. The first and second air rooms communicate with each other through passages. A plurality of sucking holes are formed in the inner sole layer to communicate air to throughholes provided to the first air room. First and second buffering members are incorporated in the first and second air rooms, respectively, to alleviate shock and circulate the air. In addition, a first check valve is disposed in the front of the second air room to open and close the passages and a second check valve is disposed in the rear of the second air room to communicate with the outside so as to discharge the air.
Each of these publications is incorporated herein by reference in its entirety.